Abstract [en]

We consider steam explosion in stratified melt–coolant configuration. Such configuration, with a liquid corium layer covered by water on top, can be formed in severe accident scenarios (i) with vessel failure and release and spreading of superheated corium melt on a floor of a shallow water pool; (ii) with melt release and spreading in initially dry cavity later flooded with water from the top. In several previous assessments of stratified steam explosion energetics, it was assumed that melt-coolant interface is initially stable and there is no premixing prior to the shock wave propagation. This assumption was instrumental for the conclusion that amount of energy released in stratified steam explosion is limited and steam explosion in such configuration is not of safety importance. However, several recent experiments carried out in Pouring and Under-water Liquid Met Spreading (PULiMS) facility with up to 80 kg of superheated, binary oxidic corium simulants mixtures have resulted in spontaneous explosions with relatively high conversion ratios (about one percent). In apparent contradiction with the previous assumptions, the instability of the melt interface and formation of premixing layer were regularly observed in the tests. In this work we presents results of the recent experiments carried out in Steam Explosion in Stratified melt-coolant configuration (SES) facility in order to shed some light on the phenomena and assess the influence of test conditions on the steam explosion energetics.